Knocking Sound



jwroubaix

Member
Jun 6, 2007
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I'm trying to diagnose a noise coming from my drivetrain. It's a knocking sound/creaking sound. I've put the bike on a stand but it doesn't do it. It also doesn't do it when i'm standing on it. Only when I'm sitting. Where do I even start? I'm obviously not a bike tech, should I just take it in? I have tried doing an extensive cleaning and re-oiling everything but it hasn't helped.
 
Originally Posted by jwroubaix .

I'm trying to diagnose a noise coming from my drivetrain. It's a knocking sound/creaking sound. I've put the bike on a stand but it doesn't do it. It also doesn't do it when i'm standing on it. Only when I'm sitting. Where do I even start? I'm obviously not a bike tech, should I just take it in? I have tried doing an extensive cleaning and re-oiling everything but it hasn't helped.
Those sounds often come from the BB or pedals. Make sure all the threads etc.. are lubed well. If it only happens while sitting, start with your seat.
 
" It also doesn't do it when i'm standing on it. Only when I'm sitting. Where do I even start?"

Are you certain it is coming from your driveline and not the seat?

Take the chain off the chainrings and spin the crankset. It should spin smoothly with no drag, grinding noises, roughness and it should not have any endplay or shake/looseness between the spindle and bearings. If it has any of those symptoms, it is due for service.

Same goes for the pedals. They should spin easily, smoothly and with no play.
 
Since it only makes the noise when you're sitting, I'd look first at the seat and seatpost. See if you can replicate the noise without pedaling, just by bouncing, rocking or twisting your bodyweight on the seat. Might be a simple as removing the saddle, greasing the rails, and reinstalling.
 
I took it out for another spin today, it is doing it when i'm standing. I still can't figure out what it is though. I have it on the stand and it doesn't when i'm moving the cranks. It must be that the pedals and or crank need weight on it to make the sound.
 
This is going to be difficult to diagnose over the 'net.

I assume the noise is associated with pedaling, not coasting - right? Does the sound always come during a particular part of your pedal stroke, is it dependent on how much force you apply. Is the noise present if you ride no handed (or very lightly on the handlebars.)

Creaks and noises can come from several places, I my experience it always at a joint of some type. Here are a few places to look:

Bottom bracket
Chainring Bolts
Quick release
Rack connections - if any
Seat rails
Seat post
Stem
Pedals